You don’t know who you’re talking to, which means you don’t have to filter out what you say as opposed to what you can/cannot say to your friends or family.
Also, reddit has so many subreddits on different subjects which helps you being able to talk to someone about a particular subject you can’t with other people.
You’re friends don’t like avatar the last air bender, there’s a subreddit full of people you can talk to about it.
You’re friends don’t like football, there’s an NFL subreddit to discuss all that’s gone down on Sunday.
You can always find someone to talk to about whatever you want as opposed to not having anyone to discuss things with in the real world.